High frequency sound translating device



June 27, 1967 w. HECHT HIGH FRQUENCY SOUND TRANSLATING DEVICE Filed Jan.@1964 SEE.

INVENTOR HECHT Mam W United States Patent 3,328,537 HIGH FREQUENEY SOUNDTRANSLATING DEVICE William Hecht, 11 Normandy Terrace, West Orange, NJ.07057 Filed Jan. 9, 1964, Ser. No. 336,682 7 (Zlaims. (6i. 179115.5)

This invention relates generally to high frequency sound translatingdevices, and particularly to diaphragm constructions for such devices.

It is an object of this invention to provide a high frequency soundtranslating device which is non-resonant at all frequencies within itsnormal range of frequency operation.

It is also an object of this invention to provide a composite diaphragmwhich has a self-sustaining, foraminous support component which isnon-resonant, and an attached diaphragm component which is likewisenonresonant.

It is another object of this invention to provide a composite diaphragmwhich will consist of non-resonant components, one of which provides anon-rigid, self-sustaining support, and the other of which is capable ofmoving air.

Yet another object of my invention is to provide a diaphragm for a highfrequency sound translating device which has a high degree ofcompliance.

A still further object of my invention is to provide a spacer for thevoice coil and diaphragm assembly of a high frequency sound translatingdevice.

These objects and advantages as well as other objects and advantages maybe attained by the device shown by way of illustration of the inventiveconcept in the drawings in which: I 7

FIGURE 1 is a vertical sectional view of the entire assembly of the highfrequency sound translating device;

FIGURE 2 is a top plan view of the rubber spacer;

FIGURE 3 is a partly exploded, elevational view of the diaphragm andvoice coil assembly; and

FIGURE 4 is a perspective view of the high frequency sound translatingdevice with the voice coil and diaphragm removed.

Sound translating devices usually employ a rigid, impenetrable diaphragmto move air in response to electrical impulses. High frequencytransducers now in general use may employ a thin, shell-like, rigid,convex dome as the diaphragm. Rigid diaphragms will inevitably resonateand will color the signal or tone produced by the electrical impulse, sothat they will not accurately re-create the original sound correspondingto the electrical impulse. On the other hand, a soft, convex diaphragmis too readily deformable, by the resistance and inertia of the aircolumn which it must move, to produce any appreciable sound. While thesoft diaphragm will not resonate, it also will not produce anysignificant sound. The utility of the vast area of diaphragrns havingintermediate qualities between softness and rigidity has remainedlargely unexplored until the present discovery. It has been found thatit is possible to produce a composite diaphragm for the reproduction ofhigh frequency sound which is sufficiently dense and rigid to producesignificant volumes of sound, yet is sufliciently non-resonant withinthe frequency range of its operation that it will not color the signalthat it translates from electrical impulse to sound vibrations. This isaccomplished by providing a non-resonant composite diaphragm which issufiiciently rigid to move air, and yet be non-resonant in its frequencyrange of operation.

A woven fabric, preferably cotton sheeting, having about 64 threads perinch of warp and 64 threads per inch 3,328,537 Patented June 27, 1967 ofwoof, is suitable for preparing a support for the diaphragm. Thematerial is not initially self-sustaining, but is limp and foraminous.It is coated with a thin layer of epoxy resin. Many other suitableresins are Well known to the industry. The material is then placedwithin the complementary parts of a die having cavities to form a domeapproximately two inches in diameter and approximately three-quarters ofan inch high. Heat is applied for a sufficient period to set the resin,and the dome is removed from the die.

The resin is used only to give the fabric a self-sustaining character.The resin is not applied thickly enough to close the interstices of thefabric. After the support is set by the resin, a thin film of fluidizedrubber or similar rubber-like material is then sprayed or brushed on thedome to close the interstices. This is allowed to dry to a thin film.This thin film of rubber on the support defines a radiating area in thediaphragm that moves the air. It

is non-resonant.

The domed composite diaphragm produced will be selfsustaining, willyield slightly to pressure in excess of 1% ounces, but will exertincreasing resistance after being depressed approximately of an inch.Greater pressure must be exerted in order to produce additionaldeformation. Although its rigidity is slight, it is sufficient torestore it to its original convexity. The preferred degree of rigidityattained through use of the resin can be easily determined byexperimentation. Too thick a coat of resin, will produce a hardunyielding dome support for the diaphragm which will resonate and give acolored response. On the other hand, too little resin will provide asupport for the diaphragm which is not sufliciently self-sustaining toreturn to its original convex shape when deformed lightly by manualmanipulation. The interstices of the fabric is closed by the rubber filmso that the dome is impenetrable by air and can move an air column.

The diaphragm to be utilized is thus a composite structure, respectingwhich composite structure, the resin impregnated fabric dome is thesupporting component of the composite diaphragm. The support is free ofresonance characteristics and yet highly responsive to migrations of thevoice coil to which it is attached.

The second component of the diaphragm is the thin rubber film which isnon-resonant and flexible when applied to the support. Rubber, or anyrubber-like material is suitable as the second component or lining ofthe composite diaphragm. By itself, this material is non-resonant, butso flexible as to be incapable to move a column of air and accurately tofollow the excursions of a voice coil because it is too readilydeformable, and totally lacks any rigidity. When applied to the slightlyrigid support, which is non-resonant, it forms a diaphragm of suflicientrigidity to move air at the predetermined high frequency range. Thesupport and film-lining do not together have a resonance period of anymeasurable degree sufiicient to color the transducers response in thefrequency range of operation.

Referring now to the drawings in detail, a magnet 11 with a generallycircular pole piece 9 is provided and a corresponding complementary poleplate 12 having a central aperture 13 in general opposition to thecircular pole piece 9. A magnet keeper 10 spans the distance between thepole plate 12 and the magnet 11. The air gap 13 between the pole piece 9and the pole plate 12 is .040 of an inch. A composite diaphragm 14 isprepared in accordance with the foregoing procedure. The edge of thecomposite diaphragm 14 has a short flange 8 to which is cemented theupper portion of a voice coil 15. The voice coil has twolayers of turnsof Wire and the outer layer is slightly shorter by a few turns than theinner one to provide an attachment seat for the flange 8. (See FIGURE3.) The adjacent turns of Wire of the voice coil 15 are adhered to eachother to form a strong, rigid, tubular coil. This voice coil 15, isdimensioned to surround the circular pole piece 9 of the magnet 11. Theexternal diameter of the pole piece 9 may be 2.000 inches. The internaldiameter of the voice coil 15 may be 2.035 inches and its externaldiameter 2.045 inches. The spider 16, or spacing member is made ofrubber, or rubber-like material, which is highly compressible. The mainbody of the spider 16 is about an inch in diameter, .019 to .020 inchthick and has 16 radial, integrally formed legs 17, each of an inch wideand /8 of an inch long. The spider 16 lies on top of the pole piece 9with the legs 17 extending down along the magnet 11. When the pole piece9 is embraced by the voice coil 15, the legs 17 of the spider 16 will beengaged generally between the internal surface of the voice coil 15 andthe pole piece 9, extending along the sidewall 18 of the magnet 11. Theinternal diameter of the aperture of the pole plate 12 is 2.080 inches,providing adequate, but close clearance for the voice coil 15. The voicecoil may be made of #35 wire, rendered self-sustaining by theapplication of lacquer or similar material in the conventional manner.The spider 16 is seized only lightly by the voice coil 15, and issufficiently compliant to permit excursions of the voice coil 15 inresponse to the magnetic driving forces. The leads 19 from the voicecoil are preferably extended through the diaphragm 14, A mounting plate20 is attached to the pole plate 12.

The slightly rigid, resilient, fabric, composite diaphragm 14 with thesoft film diaphragm overlying the fabric interstices is free ofmeasurable resonance within the range of its normal operation, 2,000 to18,000 c.p.s. and the spacing spider permits a high degree ofcompliance, resulting in an uncolored response through complete absenceof resonance of the diaphragm.

The foregoing description is merely intended to illustrate an embodimentof the invention. The component parts have been shown and described.They each may have substitutes which may perform a substantially similarfunction; such substitutes may be known as proper substitutes for thesaid components and may have actually been known or invented before thepresent invention; these substitutes are contemplated as being withinthe scope of the appended claims, although they are not specificallycatalogued herein.

What is claimed:

1. A high frequency sound transmitting device comprising:

'(a) a pair of complementary pole pieces of a magnet defining agenerally circular air gap between them,

(b) a voice coil operably positioned in the gap,

(c) a fabric dome defining a diaphragm attached to the voice coil andpositioned beyond the air gap,

(d) a coating on the diaphragm imparting a slightly rigid, resilient,yieldable, self-sustaining character and leaving the fabric intersticesopen,

(e) a soft film adhering to the diaphragm, defining a radiating area andrendering it impenetrable to air, and closing the fabric interstices,

(f) a means for supporting the diaphragm and voicecoil assembly.

2. A high frequency sound translating device comprising:

(a) a device according to claim 1, in which the coating is athermo-setting resin.

3. A high frequency sound translating device compris ing:

(a) a device according to claim 1 having no substantial resonance in therange of 2,000 to 18,000 c.p.s.

4. A high frequency sound translating device compris- (a) a deviceaccording to claim 1, in which the film is rubber.

5. A high frequency sound translating device comprising:

(a) a composite diaphragm including a support formed of a soft drapablefabric dome,

(b) an impregnation of the fabric of the dome to render itself-sustaining, slightly resilient, and readily deformable, and

(c) a soft film on the fabric to render it impenetrable to air,

((1) a means to support the diaphragm.

6. A high frequency sound translating device comprising:

(a) a pair of complementary pole pieces of a magnet defining a generallycircular air gap between them,

(b) a voice coil operably positioned in the gap,

(c) a fabric dome attached to the voice coil and positioned beyond theair gap,

(d) a coating on the fabric insufficient to fill the interstices andimparting a slightly rigid, resilient, selfsustaining character andsubject to deformation upon the application of approximately 1% ouncesof pressure, and defining a diaphragm support,

(e) a soft continuous film adhering to the fabric diaphragm, defining aradiating area and rendering it impervious to air, and defining adiaphragm-component of a composite diaphragm,

(f) a means for supporting the diaphragm and voicecoil assembly.

7. A high frequency sound translating device comprising (a) a voicecoil,

(b) a fabric dome attached to the voice coil and defining a diaphragm,

(c) a coating on the fabric diaphragm imparting a slightly rigid,resilient, yieldable, self-sustaining character, and leaving the fabricinterstices open,

((1) a soft film adhering to the fabric diaphragm defining a rediatingarea and rendering it impenetrable to air, and closing the fabricinterstices.

References Cited UNITED STATES PATENTS 1,926,187 9/1933 Young 179115.52,303,989 12/1942 Cunningham 179-1 15.5 2,502,853 5/1950 Keddie 179115.52,812,825 11/1957 Matthews 179-1 15.5 2,818,130 12/1957 Whiteley 181-32FOREIGN PATENTS 106,394 5/ 1927 Austria. 713,126 8/1931 France.

KATHLEEN H. CLAFFY, Primary Examiner.

F. N. CARTEN, A. MQGILL, Assistant Examiners.

7. A HIGH FREQUENCY SOUND TRANSLATING DEVICE COMPRISING (A) A VOICECOIL, (B) A FABRIC DOME ATTACHED TO THE VOICE COIL AND DEFINING ADIAPHRAGM, (C) A COATING ON THE FABRIC DIAPHRAGM IMPARTING A SLIGHTLYRIGID, RESILIENT, YIELDABLE, SELF-SUSTAINING CHARACTER, AND LEAVING THEFABRIC INTERSTICES OPEN, (D) A SOFT FILM ADHERING TO THE FABRICDIAPHRAGM DEFINING A REDIATING AREA AND RENDERING IT IMPENETRABLE TOAIR, AND CLOSING THE FABRIC INTERSTICES.